| Electronics > Repair |
| Korad KA3005P power supply faulty/repair |
| << < (4/27) > >> |
| alm:
How about U5-U7 (top right in the second picture)? Can't read the markings, but they look like they might be op-amps to me. Three dual op-amps is plenty for a linear bench supply with an analog regulation loop. |
| mos6502:
Right. But they could also be level shifters/buffers for the R2R DAC. IMHO the 100ms transient response (no opamp is THAT slow) and the steps in the voltage after turn-on (watch Dave's video) speak a clear language. Unfortunately Dave didn't do a transient test. Anyone who owns one of these want to do one? All you need to do is to connect a big resistor to the output and switch it with a MOSFET at ~100 Hz and trace the output voltage on a scope. I'd love to see a schematic for this thing. These are the cheapest 30V/5A PSUs out there. You can get a KA3005D for 65 Eurobucks here in Germany. But it looks like you'd have to do some major hacking and add your own regulation circuit. |
| alm:
I agree with you about the slow transient response, suspicious turn-on behavior and that putting an MCU in the regulation loop would be a bad idea, but without a schematic or someone reverse-engineering the design there is no way to be certain. The slow transient response could also be a really over damped loop response (at least it won't oscillate), for example. |
| Electro Fan:
--- Quote from: mos6502 on October 23, 2013, 12:05:03 am ---Anyone who owns one of these want to do one? All you need to do is to connect a big resistor to the output and switch it with a MOSFET at ~100 Hz and trace the output voltage on a scope. --- End quote --- +1 on this request/suggestion |
| cavlovic:
--- Quote from: mos6502 on October 22, 2013, 11:38:03 pm ---Is there another PCB in there with opamps? Because it doesn't look like there's analog regulation circuits on there. Could it be that the KA3005 uses the microcontroller to do the actual regulation? I looked at the Korad website, and the specs say that the transient response is 100ms. Yes, milliseconds! That's around 1000 times slower than a proper linear supply. Unless that's an error, that would indeed mean that the micro does the actual regulation. Which would be insane, and horrible, and make this supply all but useless except maybe for battery charging. I watched Dave's review and the steps in the voltage response would also point towards that. Anyone have a schematic for this piece of ... kit? --- End quote --- Nope, this is the only board with opamps. I would also like to know if anyone has schematics for this power supply. I couldn't find it anywhere. Once again, the board: Parts: U5-U7: dual opamps TL082C: U12: darlington transistor array ULN2003A: U13: ATMEL364:look previous at picture with your head or monitor upside down :-DD. When unit is powered on and my LED lighting pulling 1.4amps at 12V (12V set to power supply), voltage reading jumps around at the unit, but multimeter shows exactly 12v. Current readings on the power supply are fine. When I put my finger on R10-R17 (right above 4 caps in first picture) and thus heating them up and increasing resistance, voltage drops on power supply, with it the current. From 12V and 1.4amps I managed to bring it down to 11V and sub 1amp. This may tell you a little more about regulation loop. Any further help is very much appreciated. Thank you all, Balsa |
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